Skylark
I too have an A-S 55 with a broken conrod ser. # 544. I do have both pieces of the conrod though. I made a new conrod from 6061 aluminum bar stock. The new conrod is not as pretty as the stock one but the engines runs now. It has been several years ago since I made that little conrod so I do not remember the dimensions. I might be able to do a sketch of the conrod and send that to you if that will help. My workshop is in the snow at the moment and too cold to go out there. A search on Google for Allbon-Saunders was interesting:
http://www.antiquemodeler.org/sam_ne...ves_larkin.pdf
Bobbycab1
The tank on the A-S 55 looks like it made from spun aluminum and not machined from bar stock. You should be able to find some modeler over there in England that has a metal lathe that can make you one from bar stock that looks the same. I never used that type of tank on those engines because they leaked badly.
Jct049
Norfolk Aeromodelers
http://control-line.tripod.com/